1. Field of the Invention
The invention relates to a lens control apparatus, an image pickup apparatus, and a lens control method which are used in, for example, a digital VCR or the like integratedly having an image pickup apparatus.
2. Description of the Related Art
In a zoom lens system of a 4-group inner focusing type which is used in a digital VCR or the like integratedly having an image pickup apparatus, in order to change a magnification of a picture by zooming, namely, by moving a zoom lens (also called a variator) while maintaining an in-focused state, a focusing lens has to be moved along a predetermined locus. Such a locus is called a zoom tracking curve.
The zoom tracking curve usually changes depending on a distance to an object to be photographed. In the actual lens control, therefore, several typical zoom tracking curve data at several kinds of typical distances is stored in predetermined means and, with respect to distances other than the typical distances, a focusing lens position is controlled on the basis of the typical zoom tracking curve data.
For the purpose of further improving a picture quality, adding a new function, or the like, there is a case where a construction to insert and remove a filter into/from an optical path of the zoom lens system of the 4-group inner focusing type is added.
Since the nature as an optical system of a lens system changes by the insertion and removal of the filter due to a factor such that a refractive index of such a filter differs from that of the air or the like, the zoom tracking curve changes. Therefore, if the focusing lens position is controlled on the basis of only either one of the zoom tracking curve data when the filter is removed and the zoom tracking curve data when the filter is inserted, an out-of-focus is caused by the insertion/removal of the filter and a problem such that the tracking performance deteriorates and the performance of the whole lens system deteriorates occurs.
To prevent such a performance deterioration of the lens system, there is considered a method whereby both of the zoom tracking curve data when the filter is removed and the zoom tracking curve data when the filter is inserted are stored and the zoom tracking curve data which is used to calculate the distance by which the focusing lens should be moved is switched in accordance with the insertion and removal of the filter.
According to such a method, however, a point that an ROM (Read Only Memory) of a large memory capacity is necessary since an amount of data to be stored increases, a point that there is a fear such that the reliability of the control deteriorates because an amount of data which is used for a calculating process is extremely large, and the like become problems. Further, there is also a case where the zoom tracking curve when the filter is inserted differs from a result of a simulation which is performed at a design stage because of a factor such as a variation in quality of the filter or the like. In such a case, there is also a fear such that the control of the focusing lens position cannot be performed at an enough high precision under the zoom tracking curve data based on the simulation result in the case where the filter is inserted.